This invention relates to an improvement in a tag pin assembly used for attaching a price tag to goods, that is, an assembly of tag attachers. More particularly, the present invention relates to a method of producing accurately and industrially a tag pin assembly having tag pins densely disposed with small gaps between them.
Tag pin is a member for attaching a price tag to goods and is also referred to as a "tag attacher". It comprises a transversely elongated, rectangular, sheet-like head, a filament portion so extended from the center of the head as to orthogonally cross the head and a transverse rod portion so disposed at the end portion of the filament portion as to orthogonally cross the filament portion, and has an H-shape as a whole. About 50 to about 200 of such tag pins are implanted to one connecting rod through connecting portions to form a tag pin assembly. Such a tag pin assembly is integrally molded from a thermoplastic synthetic resin. having molecular orientation such as nylon or polypropylene, and thereafter the filament portions are extended, their diameter is reduced as thin as a filament, and strength as well as flexibility are improved to provide a finished product.
A large number of proposals have been made for the tag pins of this kind as described, for example, in Japanese Patent Publication Nos. 45-37100 and 52-20240.
The invention of Japanese Patent Publication No. 45-37100 relates to technique of so-called "inter-mold stretching", which utilizes a mold for the purpose of molding and as a clamping device as a part of stretching machine. A crude material of a tag pin assembly immediately after molded by injection-molding a synthetic resin such as a nylon inside the mold has a filament portion which is not yet stretched, its diameter is considerably great, its molecules have large proportions of amorphous portions, and its strength is not sufficiently high. Accordingly, such a tag pin cannot yet be utilized as the tag pin. Accordingly, this crude material is loaded into a stretching machine and the filament portion is stretched by 3 to 4 times, so that it becomes as thin as bristles and its strength and tenacity are improved. In this way, the finished product can be obtained.
However, the method which withdraws the crude material of the molded tag pin assembly from the mold and then loads it to the stretching machine so as to stretch the filament portion requires two process steps of the molding step and the stretching step, and the crude material of the tag pin assembly having a delicate structure must be transferred between these two process steps. Accordingly, defective products are likely to occur. In the actual production process of the tag pins, however, the machining speeds and the control conditions are entirely different between the molding step and the stretching step. For this reason, machining is mostly carried out by installing the respective machines for the respective steps in different plants.
In the invention of this Japanese Patent Publication No. 45-37100, the mold used for molding is split into upper and lower units (or into the right and left units) and is further split into the right and left units (or into the upper and lower units) at the intermediate portion of the filament portion from the parting line, so that the same mold used for molding can be used consecutively for stretching. In other words, the reference invention uses, in principle, a 4-split mold, allows the other mold to move with respect to one of the molds which clamps the filament portion, and consecutively stretches the filament portion while the crude material of the tag pin assembly produced by the molding step is kept retained inside the mold. This reference invention provides an excellent apparatus that can produce a delicate tag pin assembly highly efficiently in that the crude material of the tag pin assembly can be processed to a finished product without withdrawing it from inside the mold.
On the other hand, the invention of Japanese Patent Publication No. 52-20240 provides a "connecting pin" which can prevent entanglement of heads of a tag pin assembly. As described above, in the tag pin assembly, a large number of tag pins are implanted to one connecting rod through connecting portions, and the tag pin assembly has a comb-shape as a whole. Generally, the heads are separated from one another and can move individually and independently.
When packaging or using the tag pin assembly, a plurality of tag pin assemblies are stored in one box. Under this state, however, the heads entangle with one another, and they must be separated one by one when they are loaded into a fitting machine and are used in practice. This reference invention provides an excellent solution to this problem by connecting the heads to one another by an easily tearable connecting member and integrating the heads into a mass.
As can be seen by referring to the accompanying drawings of this Japanese Patent Publication No. 52-20240, cavities engraved in a mold are arranged transversely with a sufficient gap as wide as the thickness of each head. The tag pin assembly is molded from a thermoplastic resin such as nylon or polypropylene, and an injection molding pressure as high as about 700 to about 1,500 kg/cm.sup.2 is necessary for this molding step.
Accordingly, walls capable of withstanding this high pressure are necessary between the cavities for molding the individual tag pins. More specifically, in the case of a mold wherein cavities for a tag pin assembly are engraved in a mold steel stipulated in JIS SKD61, the gaps between the tag pins, that is, the thickness of the walls defining the chambers for storing a resin during molding, poses a problem.
In a conventional mold, one gate is provided to one connecting rod. Therefore, the resin for molding 50 to 200 tag pins is supplied through one gate and one connecting rod.
For this reason, a minimum thickness of the walls of about 1.0 to about 1.2 mm is necessary lest the walls defining the cavities are broken even when any small pressure difference exists between the molten resin packed into the cavities of the tag pins adjacent to one another. Such a limitation makes it extremely difficult to remarkably reduce the pitch of the tag pins.
To facilitate packaging and transportation of the tag pin assemblies and their loading into and operation of the fitting machine, on the other hand, the tag pin assembly must be made compact in size by reducing the gap between the heads and that between the transverse rod portions. In other words, a tag pin assembly having a dense and delicate structure is necessary, and various attempts have been made in this point. As described above, however, the gap of about 1.0 to 1.2 mm is necessary between the individual cavities for molding the tag pin assembly, or in other words, the thickness of the walls defining the cavities, is necessary. If the walls are thinner than the value described above, they are highly likely to be broken by the pressure of the injected resin and even if they are not broken, they cannot withstand repetition of stresses applied many times, and durability is therefore low.
Generally, a mold used industrially used for producing the tag pin assembly must withstand at least 10,000,000 shots from the aspect of the production cost of the mold.
Another problem is as follows. The connecting rod connecting 50 to 200 tag pins into the assembly is an important member corresponding to a runner portion through which large quantities of the resin flows during molding, and the resin injected for this connecting rod is branched and supplied into the cavities for the individual tag pins. In other words, the molten synthetic resin is supplied from one gate to one runner portion, is branched from the runner portion and is then supplied into the cavities for molding the individual tag pins.
In the case of the conventional tag pin assembly which is sold in quantities and wherein the tag pins are disposed on one connecting rod with a pitch of about 2 mm, the molten resin tends to flow substantially uniformly into the cavities for the individual tag pins. In other words, it has been confirmed that insufficiency of the molten resin in part of filament portions hardly occurs, and a defect ratio is low.
However, when the gap between the tag pins is gradually decreased so as to make the tag pin assembly more compact in size, a delicate unbalance occurs in the amount of the resin flowing into the filament portions, defects occur at the filament portions and in some case, cut-off of the supply of the resin occurs.
FIGS. 13, 14, 15 and 16 of the accompanying drawings correspond to FIGS. 5, 6, 7 and 8 of Japanese Patent Publication No. 37100/1971, respectively. The conventional method of producing the tag pin assembly by the "inter-mold stretching method" will be briefly explained with reference to these drawings.
The mold comprises four units, that is, upper molds 10, 10a and lower molds 11, 11a, and is split to the right and left from the parting line PL in such a manner that the other set of molds 10a, 11a can be moved with respect to one of the sets of the molds 10, 11 and stretch the filament portions 2. During molding, the split molds shown in FIGS. 13 and 14 gather together and define the cavity of the tag pin assembly P of the tag pins p each comprising the head 1, the filament portion 2, the transverse rod portion 3 and the connecting rod 5.
To begin with, while the four molds are gathered as shown in FIG. 14, the molten resin is injected into the cavity and the crude material of the tag pin assembly P is molded. Next, as shown in FIG. 15, the molds 10a, 11a are separated from the parting line PL and are moved in the transversely direction while the molds 10 and 11 are kept fixed as shown in FIG. 15, so that the filament portions 2 are stretched to a predetermined length and made thinner, and the strength is improved.
Next, ejector pins 12, 12a are brought into contact with both ends of the head 1 and other ejector pins 13, 13a are brought into contact with both ends of the transverse rod portion 3 as shown in FIG. 16. While the crude material of the tag pin assembly P is kept adhering to the lower mold side in this way, the upper molds 10, 10a are raised and the split faces in the vertical direction of the molds 11, 11a, 10, 10a are opened.
The ejector pins 12a, 13a provided to the lower mold side 11, 11a are protruded upward and the tag pin assembly P is withdrawn from the mold. In this way, molding and stretching steps of the tag pin assembly P are completed. Thereafter, portions unnecessary for the products such as a spool, a runner bar, etc, are automatically cut off by an ordinary post-processing method, and only the tag pin assembly P is transferred to a next step.
Next, the problems with this process will be explained in further detail with reference to FIGS. 11 and 12.
In the cavity C, each tag pin p comprising the head 1, the filament portion 2 and the transverse rod portion 3 is so disposed at to orthogonally cross the connecting rod 5 through the connecting portion 4 in match with the crude material of the tag pin assembly P (under the state where the filament portion 2 is not yet stretched). The cavity C has a comb-shape as a whole. The center portion of this connecting rod 5 and the main runner portion 6 are connected by a sub-runner portion 7, and this main runner portion 6 is connected to the spool 8 as a main flow passage of the resin injected from an injection molding machine.
In the ordinary mold, about four cavities C are disposed on each side of this main runner portion 6 and eight crude materials of the tag pin assemblies P can be molded at one time.
FIG. 12 is a sectional side view of the principal portions of this mold. The ejector pins 12, 12a, 13, 13a are disposed at both ends of the head 1 molded between the upper mold 10 and the lower mold 11 and at both ends of the transverse rod portion 3 molded between the upper mold 10a and the lower mold 11a, and these pins are constituted in such a fashion as to simultaneously project the tag pin assemblies P in the mass form after molding from the cavities and to withdraw from the mold with the main runner 6 and the spool 8 by utilizing the piston motion of a cylinder device (see FIG. 14) provided to the upper and lower molds.
The molds 10, 10a, 11, 11a are constituted in such a manner that they are separated from the parting line PL, and one of the sets of them can instantaneously move by a predetermined distance from the other set when the filament portions 2 are stretched as indicated by an arrow.
The molten resin J discharged from the injection molding machine, not shown in the drawings, flows into portions indicated by arrows a, b, d and d' through the spool 8 and the main runner 6, altogether flows into the cavities for molding the tag pins p through the connecting rod 5 as indicated by arrows e and f, and is charged while spreading as a whole.
When the gap between the tag pins p is as wide as about 2 mm as in the crude material of the conventional tag pin assembly, the resin flows correctly into the cavities C of the tag pins p.sub.1, p.sub.2, . . . , p.sub.n. Therefore, molding defects such as insufficiency of the resin do not occur and the filament portions 2 can be molded into a predetermined dimension. Accordingly, even when these filament portions 2 are altogether stretched, there does not occur the problem that a part of them is broken and effective products occur.
Recently, attempts have been made to make the tag pin assembly more compact as a whole by reducing the length of the tag pin assembly (that is, the length of the connecting portion 5).
They are primarily directed to the following points. First, the room for intrusion of other heads 1 is eliminated by reducing the gap between the heads 1 to a value smaller than the thickness of the heads 1 so as to prevent entanglement of the heads 1. Next, handling property of the tag pin assembly is improved by minimizing the portion of the tag pin assembly, which protrudes from the fitting machine and is unstable, when it is loaded into the fitting machine. Third, material is saved by reducing the length of the connecting rod. To accomplish these objects, a tag pin assembly under a ultra-close contact state or a tag attacher of a ultra-close contact type must be developed.
This ultra-close contact tag pin assembly has a by far closer and more delicate structure than the conventional tag pin assembly, and to produce such a ultra-close contact tag pin assembly, the cavities for molding the tag pins p.sub.1, p.sub.2, . . . , p.sub.n must be disposed by far more closely to one another than the conventional mold for molding the conventional tag pin assembly.
To attain this object, the problem exists in that the "thickness of the wall" defining the cavity of the individual tag pins p must be reduced to a level which is never expected in the past. However, as already described, the pressure of the high pressure molten resin repeatedly acts on the cavity, and there is a delicate difference between the flows of the molten resin charged on both sides of the wall partitioning the cavities. Accordingly, if even a slight delay exists in the flow of the resin on one of the sides of the wall, the pressure becomes higher more quickly in one of the cavities than in the other, though limitedly. Since the flow of the molten resin is rapid, the high pressure acts impulsively on this wall surface if such a pressure difference occurs.
The time in which the molten resin is injected into the cavity is very short, and it is very important to charge the resin simultaneously and uniformly into a large number of cavities. If the balance can be established somehow in the flowing condition of the resin in this case, it is possible to reduce the gaps between the tag pins by remarkably reducing the thickness of the walls partitioning the cavities. Whether or not this problem can be solved is the pressing problem for those engaged in this field of art.
In the case of the conventional tag pin assembly, the molten resin is supplied to one connecting rod from one sub-runner portion as shown in FIG. 13 of the afore-mentioned Japanese Patent Publication No. 37100/1971 and in FIG. 11 of the accompanying drawings. Therefore, a delicate difference occurs in the packing speed of the molten resin to the cavities between the portions near and far from the inflow port of the resin, and a difference occurs between pressures acting on both sides of the wall defining the cavity. However, no substantial problem has occurred such as breakage of the wall of the cavity because the gap between the tag pins is great.
The reduction of the thickness of the wall of the cavity means the reduction of the pitch of the tag pins and the formation of a more delicate tag pin assembly, and makes it possible to produce a ultra-close contact tag pin assembly which has a delicate and compact structure, is easy to use and is free from entanglement.
The present invention is completed as a result of various studies on the flow of the molten resin inside the mold and its moldability in order to solve the problems with the prior art described above, and aims at providing a method of producing a ultra-close contact tag pin assembly.